The present invention relates to a measuring instrument for checking dimensional accuracy of a surface or a toothing.
In German patent specification DE 31 09 334 C2 (Frenco) there is disclosed a device consisting of a measuring head in which is mounted a cylindrical support element for two diametrically opposite checking elements bearing against a surface or toothing, which is to be checked, of a workpiece, wherein radial movements of the checking elements caused by irregularities of the surface or the toothing are transmitted to a drive needle extending perpendicularly to the checking elements and displaceable in a central bore of the support element and the displacement of the drive needle is indicated by a measurement sensor. However, this device is subject to the disadvantage that the measuring plane of the checking elements in the workpiece cannot be measured by the device itself.
A measuring instrument for measuring the diameter and axial position of an internal annular groove is described in German specification DE 90 03 357 U1 (Kxc3xcnz), the annular groove being disposed in the cylindrical inner wall of a workpiece. The possible radial dimension and axial dimension of the annular groove can vary only within narrow tolerance ranges. The measuring instrument is therefore not in a position of measuring the accuracy-to-size of the inner diameter of a longer cylindrical space in dependence on axial position.
Moreover, in German specification DE 44 12 069 A1 (Straube) there is disclosed a manually actuable device for ascertaining deviations of a bore from the cylindrical shape, which device is provided for measuring relatively large cylindrical internal diameters of, for example, cylinder liners. In this case, the axial position of a measurement value pick-up is detected at the same time. As the entire measuring device has to be inserted into the bore, this is usable only for measurement of cylindrical spaces with a large internal diameter.
It is therefore the object of the invention to provide an instrument for checking dimensional accuracy of cylindrical surfaces or toothings, the instrument also being usable in the case of a large ratio of length to diameter of the cylindrical surface and being able to measure accuracy-to-size over approximately the entire length.
According to the present invention there is provided a measuring instrument for checking dimensional accuracy of a surface or a toothing of a workpiece, the instrument comprising a handgrip, an inner cylinder member rigidly connected with the handgrip and extending therefrom to have a free end, the handgrip and the inner member defining a substantially cylindrical space therebetween, an outer cylinder member mounted in said space to be displaceable relative to the inner cylinder member when urged against said workpiece, resilient means providing a bias to resist said relative displacement of the inner and outer cylinder members, a measuring head mounted at said free end of the inner cylinder member, a carrier element mounted in the measuring head and defining a central bore having a bore axis, two diametrically opposite checking elements mounted in the carrier element to be radially movable with respect to said bore axis in response to dimensional variations in a workpiece surface engaged by the checking elements, a movement translation member extending substantially perpendicularly to the checking elements and movable in the bore in response to said radial movement of the checking elements, a measurement sensor mounted in the inner cylinder member remote from said free end thereof and responsive to said movement of the translation member to provide a measurement indicative of said movement of the translation member, and a travel sensor responsive to said relative displacement of the inner and outer cylinder members to provide a measurement indicative of said relative displacement.
Preferably, each of the measurement sensor and the travel sensor comprises a respective electronic component. The instrument can include means to prevent relative rotation of the inner and outer cylinder members. Moreover, support means can be arranged on the outer cylinder member to support the instrument on said workpiece.